Thermocontrol arrangement for electric circuits



June 19, 1951 E. A. CHANDLER TI-[ERMOCONTROL ARRANGEMENTS FOR ELECTRIC CIRCUITS Filed May 19, 1947 @attended Liane i9, 395i narran sri-aras PTEN? THERMOCNTROL GEMENT FR ELECTRIC CRCUITS Edward Anthony Chandier, Londen, Engiand, as-

signer to Molins Machine Company Limited,

London, England, a

British company Application May 19, 1947, Serial No.

In Great Britain 149,048 May 20, 1946 Claims. (C1. 2175-375) This invention concerns improvements in or relating to thermo-control arrangements for electric circuits and According to the invention there is provided a thermo-control arrangement for an electric circuit comprising a, relay adapted to-controi the c rent in said circuit (e. g. to make and break the circuit), a thermostat located in a position ond being adapted to be closed by in the relay coil.

The rst and second switches may be operated to make and break the relay circuit by means of electric heaters 5 the wheel is empty and there are no packets to is fitted to the machine at a suitable position near the heaters.

The invention with reference to the which- Figure 1 is a diagram illustrating the invention.

Figure 2 is similar to Figure 1 but shows a ferent method of operating the timing switch.

Figure 3 is similar to Figure 1 but shows a further method of operating the timing switch.

Referring to the drawings:

The thermometer cons' ts a tube 2 with several platinum contacts such as 3 and 4 sealed in the tube and disposed at various heights in the tube to give several possible temperature ranges according to which pair of contacts is connected to the circuit. The mercury is deliberately shown low in the tube so that the thermometer contacts can be seen. The upper thermometer contact 3 is connected to one lead, e. g. the negative, of a low-voltage circuit, the voltage being pro ded by a battery 5, for instance at a pressure of two volts. The thermometer contact 4 is connected to a pivoted arm 6 having a contact 1 which is operated periodically by movements oi the arm 6 as described later to cooperate with a contact 8, thus forming a switch.

The contact 8 is on a pivoted arm 9 from which a line leads to one end of the coil I of a relay. The relay consists of the coil and two movable arms I and I8 each having a contact, I4 and I6 respectively, adapted to engage with other contacts, I3 and I1 respectively, thus constituting two separate switches described and referred to later as the first and second relay contact switches. From the other end of said relay coil a line leads to the other pole of the battery, e. g. the positive side. Another contact II joined to the second contact 8 (i. e. carried on the arm 9) is provided which is periodically connected to a further contact I2 by movementsV of the arm 9, the contacts II and I2 thus forming a further switch. From the contact I2 a line leads to the contact I3 of the first relay contact switch. From the arm I5 a line leads to the negative side of the battery. Since the whole switch device comprising the four contacts 1--8 and II-I2 is operated periodically it will be, for convenience, referred to comprehensively as the timing will be more fully described accompanying drawings in of a bulb I andv switch, T, while the said first relay contact switch (i. e. the contact I3-I4) will be indicated generally by the reference R. I.

The contacts I6 and I1 switch the main current for the machine heaters on and off and constitute a second relay contact switch and bear the general reference R. 2. A line leads from the arm I8 to the heater I9 of the machine and thence to one terminal ofy the main supply 20. The other terminal of 20 is connected to the contact I1.

As the timing switch T is operated, the iirst switch 1--8 closes and shortly afterward the second switch II-I2 opens. Thenl a moment later the second switch II--I2 closes and after a further short interval the first switch 1 8 opens. These events take place at regular intervals though neither the time of the interval nor precise regularity are of great importance and the switch movements may be effected by a cam 2I and rod 22.

As above explained the timing switch is operated periodically and the movements are such that during a time interval of 1,4,0 second in a cycle oi 10 seconds the switch 1-8 closes, then the switch II-I2 opens, next the switch II-I2 closes and finally the switch 1-8 opens. Thus if the upper contact of the thermostat is in contact with the mercury (i. e. the temperature is high) the relay coil I0 is energized when the switch 1-8 closes. Thereupon the rst relay contact switch R. I is closed and the main current or second relay contact switch R. 2 is opened and the heater I9 is switched oif.

Next the switch `I I-I2 opens. Then it closes and holds the current in relay coil I0, whereupon the switch 1-8 opens but the relay coil current is still-held by the locking circuit provided by the relay contact switch R. I, which circuit does not include the thermostat until the end of the cycle when once again control passes to the thermostat, that is the relay coil circuit will again include the thermostat.

On the next cam rod stroke, that is. at the next cycle, supposing the temperature is still high, nothing further happens, for the closing of switch 1 8 maintains the relay coil circuit during the time that switch II-I2 opens and when the latter closes and 1-8 opens, the relay coil remains energized through switches II-I2 and I3-IIL As the mercury column falls in response to a fall in temperature oi the heated parts of the machine the upper contact 3 of the thermostat will eventually become exposed as the mercury falls and if the current is on, an arc will occur between the mercury and said contact 3 which will break in time when the length is too great for the arc to persist. Arcing also occurs as the column rises toward a contact. This arcing causes the contacts to corrode and the products of combustion of combination between the mercury and the platinum contacts dim the tube of the thermometer and obscure visual reading. The present invention reduces the chances of arcing occurring since the time interval when the thermostat is in circuit is very small indeed and it is only rarely that the mercury is approaching or receding from the upper contact in such manner that arcing can occur at the instant the voltage is applied to the thermostat.

Supposing then that the temperature has fallen before the beginning of the next cycle sufficiently to expose the upper thermometer contact 3, the closing of the switch 1-8 will have no result as the corresponding circuit through the relay is broken in the thermostat. When, however, the continued movement of arm 6 opens switch I I'-I 2 the existing relay coil circuit, which is holding arms I5 and I8 up, is broken and they drop. The heater I9 is therefore switched on while the relay coil remains dead until the next cycle when events will occur as noted above according to whether the thermometer contact 3 is in or out of the mercury.

It will be seen then that the thermostat may be in circuit for a very small proportion of the time the machine is wor g and it is only on very rare occasions that the mercury would rise to or sink below a contact at the precise instant that the current is on, so arcing may be said to be nonexistent for all practical purposes.

In a specific case the time allowed for the rst switch 1-8 to close is 3 milli-seconds though it can be shorter. The second switch II-I2 then opens and stays open for a further 14 milli-seconds. This period is sufficient to allow the relay to operate (i. e. for the arms I5 and I8 to move away from the coil) in the case where temperature has fallen low enough for the mercury to be below the thermostat contact 3, when it is necessary for the relay coil i to be switched off so that the main current contacts of the relay contact switch R. 2 will be closed and the heaters milli-seconds period, may however be shorter, the rst switch 1 8 opens. The switch Il-IZ remains closed until the start of the next cycle, and then opens again which is suillcient to ensure operate if a current passes.

iirst relay contact switch R. of a cycle may be `closed or open according to the events of the previous cycle but if it is closed (when the second relay contact switch that the relay will 'I'he position of the I at the beginning sequent opening of the switch |||2 breaks the only remaining current through the circuit. Conversely if the iirst relay contact switch R. I is open (heaters on) and lower limits of temperature.

There are numerous ways in which the timing switch may be operated and the method chosen depends on the best available means.

the voltage starts to build up again. The disthrough the neon tube can tion.

be used with other forms of thermostat where desired, for example a bimetallic strip.

The term switch includes any device for making and breaking an electric circuit.

What I claim as my invention and desire to secure by letters Patent is:

l. In a thermostatically controlled relay sysgized from said relay energizing circuit only during a period of conjoint closure of said thermostatic and normally open switches, and is thereafter energized by said relay holding circuit until released by conjoint opening of said thermoswitch contacts is thereby prevented.

2. A system as claimed in claim 1 including devices mechanically coupling said normally open and said normally closed switches to eil'ect operasystem as claimed in claim 1 wherein said means is constituted by a thermal relay EDWARD ANTHONY CHANDLER.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,347,514 Shively et al. Apr. 25, 1944 2,363,433 Olson Nov. 21, 1944 2,435,027 Blomberg Jan. 27, 1948 2,463,469 Schirokauer Mar. l, 104! FOREIGN PA'I'ENTs Number Country Date 67,855 Sweden Apr. 21, 1938 

